Help on Graphical Interval Selection Widget

Left-click on the plot to define the start of an interval, right-click to 
define the end of that interval.

If the 'Contiguous intervals' option is selected, once you've defined an 
interval, another right-click to the right of that interval will define 
the end of a new interval whose start is the end of the previous interval.

If the 'Force to data boundaries' option is selected, every interval 
boundary you define will be forced to line up with the nearest data 
accumulation boundary.

Left double-click in any interval to bring up a menu of options for 
editing that interval, or breaking it up into sub-intervals.  

The 'Adjust to data boundaries' button examines all of the currently 
defined intervals, and adjusts them so that they are aligned with data 
accumulation boundaries.


Notes:

If you left-click twice in succession (without right-clicking in between),
the first click is ignored, and the start moves to the location of the 
second left-click.

Right-clicks to the left of where you left-clicked (i.e. the end before
the start) are ignored.